From c3f403419981e1e77223fc0a8707b18bcaae61e4 Mon Sep 17 00:00:00 2001
From: James Rodewig <james.rodewig@elastic.co>
Date: Wed, 24 Jun 2020 17:21:26 -0400
Subject: [PATCH] [DOCS] Note that DS timestamp field mapping changes require
 reindex (#58444) (#58517)

With #58096, data streams now track the timestamp field mapping outside
of the template associated with the stream. This means you can no longer
update the timestamp field mapping using template changes.

This updates the associated data stream docs.
---
 .../data-streams/change-mappings-and-settings.asciidoc    | 5 +++++
 docs/reference/data-streams/set-up-a-data-stream.asciidoc | 8 +++++++-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/docs/reference/data-streams/change-mappings-and-settings.asciidoc b/docs/reference/data-streams/change-mappings-and-settings.asciidoc
index 42edc398aa7..5313873f48e 100644
--- a/docs/reference/data-streams/change-mappings-and-settings.asciidoc
+++ b/docs/reference/data-streams/change-mappings-and-settings.asciidoc
@@ -133,6 +133,11 @@ POST /logs/_rollover/
 ----
 // TEST[continued]
 ====
++
+IMPORTANT: You cannot use these methods to change the mapping of a data stream's
+<<create-a-data-stream-template,timestamp field>>. To change the timestamp
+field's mapping, you must reindex the data stream. See
+<<data-streams-use-reindex-to-change-mappings-settings>>.
 
 * To apply mapping and setting changes to all existing backing indices and
 future ones, you must create a new data stream and reindex your data into it.
diff --git a/docs/reference/data-streams/set-up-a-data-stream.asciidoc b/docs/reference/data-streams/set-up-a-data-stream.asciidoc
index 968cb0eda95..685f6978239 100644
--- a/docs/reference/data-streams/set-up-a-data-stream.asciidoc
+++ b/docs/reference/data-streams/set-up-a-data-stream.asciidoc
@@ -138,7 +138,13 @@ this pattern.
   stream.
 
 * A <<date,`date`>> or <<date_nanos,`date_nanos`>> field mapping for the
-  timestamp field specified in the `timestamp_field` property.
+timestamp field specified in the `timestamp_field` property.
++
+IMPORTANT: Carefully consider the timestamp field's mapping, including
+<<mapping-params,mapping parameters>> such as <<mapping-date-format,`format`>>.
+Once the stream is created, you can only update the timestamp field's mapping by
+reindexing the data stream. See
+<<data-streams-use-reindex-to-change-mappings-settings>>.
 
 * If you intend to use {ilm-init}, you must specify the
   <<configure-a-data-stream-ilm-policy,lifecycle policy>> in the